Hello from eastern Oklahoma! (Have a rooster question, too.)

Hello, everyone! I grew up in eastern Oklahoma, and as a kid I had to feed and water Grandma's chickens, but I wish I had paid close attention to some of the particulars.

I recently ordered 25 Rhode Island Reds that came in the mail in an itty-bitty box. They actually gave me 28 and the chickens are 1 month 3 weeks old now, and I lost one when they were only a few weeks old ...so there are 27 now (about 20 are hens).

I made an outside building into a coop with plenty of air flow, and already put the nest boxes in.

I heard something that has me troubled. Someone told me that you don't want to use roosters that was in the same flock as the hens. Is this true? I would sure like to just keep two roosters out of this bunch instead of going off to find roosters from another place (I also want to stick with Rhode Island Red roosters).